This is a Division of application Ser. No. 10/936,509 filed Sep. 9, 2004. The disclosure of the prior application is hereby incorporated by reference herein in its entirety.
The present invention relates to a form measuring device, a form measuring method, a form analysis device, a form analysis program, and a recording medium storing the program. More specifically, this invention relates to a form measuring device capable of accurately measuring irregularities or angular displacements of each surface of a flat polyhedron, or a form measuring device capable of analytically obtaining a form of a surface.
There have been used various measuring device and measuring methods for highly precisely measuring a form of an object.
As a first example, when accurately measuring the form of an object to be measured having polygonal flat surfaces, it is necessary to precisely measure irregularities and angles of each surface of the object to be measured. For instance, when measuring a form of a right-angled square, it is necessary to measure straightness of each edge and perpendicularity of each of the four right angles.
Conventionally, straightness of each edge has been measured, for instance, by scanning an object edge to be measured with a detector (such as, for instance, an electrical micrometer) moving along a straightedge ruler to detect displacement from the straightedge ruler as a reference for straightness. On the other hand, perpendicularity has been measured by placing the right-angled square on and inside reference scales positioned with right angles to each other and measuring a distance from the reference scales to each edge of the right-angled square (Refer to, for instance, Document 1: Japanese Patent Laid-Open Publication No. HEI 9-2433351).
When measuring is performed by detecting displacement from a certain reference as described above, however, sometimes positional arrangement and posture of an object for measurement may disadvantageously be displaced against the reference in measurement, or the reference itself may disadvantageously include some manufacturing errors. When any of the displacements as described above (which are different from those occurring during measurement) exists, the displacement is included in a result of measurement, so that high precision measurement can not be expected.
For calibrating straightness, there has been proposed the three planes alignment method (three-flat method) as a measuring method not affected by a reference scale or positional arrangement and posture of an object for measurement in measurement (Refer to, for instance, Document 2: Japanese Patent Laid-Open Publication No. HEI 2-253114, Document 3: Japanese Patent Publication No. 2003-121131).
In the three planes alignment method, in each of the three pairs (A and B, B and C, and C and A) obtained by combining two of three rod-like objects for measurement (A, B, C), two objects (for instance, A and B) are placed at positions opposed to each other, and a distance between measuring surfaces facing to each other is measured at a plurality of points. Measurement of a distance between measuring surfaces is performed in each pair, and a solution satisfying the three pairs of objects for measurement is obtained through a simultaneous equation. With this operation, straightness of each object for measurement is calculated as a displacement from a virtual reference line. With the operations as described above, it is advantageously possible to assess straightness without being affected by any manufacturing error of a reference scale or positional arrangement and posture of the reference scale or an object for measurement.
With the three planes alignment method as described above, it is possible to accurately measure straightness of an object for measurement even when a scale with the straightness still unknown is used, but there is the problem that the capability is limited only to the on-dimensional calculation. In other words, there is the problem that, in relation to an object for measurement which is a flat polygon such as a right-angled square, even though straightness of each edge can be measured, perpendicularity of each angle formed with two edges can not be assessed. To overcome this problem, if it is tried to extend this one-dimensional calculation method to a two-dimensional calculation method for computing positional relations between edges, function values for solving the simultaneous equation disadvantageously increase.
In view of the circumstances as described above, it has been desired to provide a form measuring device and a form measuring method for a flat polyhedron enabling easy and high precision measurement of irregularities on and internal angles of each of the polygonal surfaces, a form measurement program for the method, and a recording medium for the program (First object).
As a second example, there has been known a method in which flatness of a surface is measured. For instance, irregularities of a surface as an object for measurement are measured against a reference surface having been processed to a completely flat surface. As the method for flatness measurement as described above, for instance, there has been known the interference method in which the space between a surface to be measured and a reference surface, both positioned substantially in parallel to each other, is measured by detecting the interference pattern as shown in FIG. 15.
In FIG. 15, an optical interferometer 100 for measuring the distance between two surfaces comprises a light source 101 as a laser beam source, a CCD camera as a photographing device, and a half-mirror 103 provided on the light axis.
A reference object 201 having a reference surface D, which has been processed into a completely flat surface, and an object to be measured 202 having a surface to be measured E are provided on the light axis of the optical interferometer 100 in the state in which the reference surface D and the surface to be measured E are positioned face to face substantially in parallel to each other. The reference surface D and the surface to be measured E are positioned vertically to the incident light from the light source 101. Both of reference object 201 and the object to be measured 202 are made of transparent material such as glass.
With the configuration as described above, when light from the light source 101 is introduced onto the object to be measured 202 and the reference object 201, interference is generated between the surface to be measured E and the reference surface D, and an interference pattern appears. When this interference pattern is observed by the CCD camera 102, spaces between the observed image and the reference surface D or the surface to be measured E are measured at each sampling point. In this step, irregularities of the surface to be measured E against the reference surface D are measured at each sampling point.
Here, it is assumed that the reference surface D has been manufactured to a completely flat surface, but it is actually impossible to process a reference surface to a completely flat surface. Since flatness of the surface to be measured E is measured based on spaces between the reference surface D and the surface to be measured E, when irregularities or undulations are present on the reference surface D, it is naturally impossible to accurately obtain flatness of the surface to be measured E.
In view of the circumstances as described above, it has been desired to provide a form measuring method capable of easily and precisely analyzing a form of a surface to be measured (second object).